This invention relates to the measurement of brain electrical activity.
Such measurement is based on the localized discrete sampling, both in space and time, of a biological variable. In multichannel evoked potentials (EPs) the underlying biological event is both space and time-variant. To analyze the scalp-recorded activity generated by such events, spatiotemporal relationships must be explicit. This is readily apparent by inspecting the dynamic evolution of topographic maps generated by even simple sensory stimulations. Although topographic maps make biological events more comprehensible, they do not simplify the quantitative evaluation of the phenomenon; on the contrary, new and more complex features are made evident. Expressions such as slowing, lateralized, persistent, focal, and asymmetrical are often used to describe these complex phenomena. Such subjective terminology may be descriptive of the findings but is not easily amenable to a quantitative evaluation. There is a need to quantify these subjective judgments. Doing so will enhance the diagnostic power of event-related potentials
Traditional analysis of EP data involees compilation of the latencies to sequential numbers of "standard" positive and negative peaks. This method of analysis has not proven useful for the purposes of topographic mapping for a number of reasons: First, many normal subjects fail to demonstrate the so-called normal peaks and valleys. Second, even for those subjects whose EPs over primary cortex are "classic" in morphology, their EPs at remote locations may appear quite complex and different from the primary response. For example the visual evoked response (Ver) recorded from the anterior temporal electrodes is never a slightly scaled down, latency stretched version of the occipital recorded response, but has its own complex morphology. Third, the presence of pathology may totally distort EP morphology rendering the recognition of standardized components difficult or impossible even over primary cortex.
Brain electrical activity mapping (BEAM) is a known diagnostic tool for detecting brain abnormalities. BEAM is described in U.S. Pat. No. 4,421,122; Duffy et al., "Brain electrical activity mapping (BEAM): A new method for extending the clinical utility of EEG and evoked potential data," Ann. Neurol., 5:309-321 (1979); Duffy, Bartels, et al., "Significance Probability mapping: An aid to the topographic analysis of brain electrical activity," Electroenceph. Clin. Neurophysiol., 512:455-462 (1981); Duffy, Topographic Mapping of Brain Electrical Activity, Butterworths (1986) (all incorporated by reference).